Fittings may be used to join or connect the end of a tube or other conduit to another member, whether that other member be another tube or conduit end such as through T-fittings and elbow fittings, for example, or a device that needs to be in fluid communication with the tube end, such as for example, a valve. One type of fitting uses a gripping arrangement including two ferrules that provide a gripping and sealing action between a tube and a body under the influence of a female threaded drive nut. Other types of fittings are also known, such as, for example, single ferrule fittings, fittings that use other types of tube gripping devices, and fittings that use male threaded drive nuts.
Tube fitting components that are radially displaced or expanded upon pull-up take up a portion of the deformation energy of pull-up and may contact radially adjacent and/or radially nearby fitting component surfaces as a result of the expansion or displacement. For example, the tubing inboard of the tube gripping member, such as, for example, the front ferrule of a two ferrule fitting or the ferrule of a single ferrule fitting, may expand radially outward during fitting pull-up and takes up a portion of the deformation energy of pull-up.